<!DOCTYPE html>
<html>
<head>
    <title></title>
</head>
<body>
  <div id="host">Shadow DOM</div>
  <script>
    const host   = document.querySelector('#host');
    const root   = host.attachShadow({ mode: 'open' });
    const header = document.createElement('h1');
    const input  = document.createElement('input');

    header.textContent = 'Test Me!';

    header.addEventListener('click', () => header.textContent = 'Test passed');

    root.appendChild(header);
    root.appendChild(input);
  </script>
</body>
</html>
